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Questions and Answers
What type of proteins regulate the formation of clathrin-coated vesicles?
What type of proteins regulate the formation of clathrin-coated vesicles?
Clathrin interacts directly with the cargo proteins in vesicle transport.
Clathrin interacts directly with the cargo proteins in vesicle transport.
False
What is the diameter range of clathrin shells?
What is the diameter range of clathrin shells?
700–800 Å
The _____ proteins direct vesicles to the correct membrane.
The _____ proteins direct vesicles to the correct membrane.
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Match the following terms with their descriptions:
Match the following terms with their descriptions:
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What is the primary function of SNARE proteins?
What is the primary function of SNARE proteins?
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Light chains are involved in the polymerization of heavy chains in clathrin.
Light chains are involved in the polymerization of heavy chains in clathrin.
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What shape do clathrin vesicles typically take due to natural curvature?
What shape do clathrin vesicles typically take due to natural curvature?
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What is the role of the trans Golgi network in protein packaging?
What is the role of the trans Golgi network in protein packaging?
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Regulated secretory pathways include the release of ions from muscle cells.
Regulated secretory pathways include the release of ions from muscle cells.
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What are sec mutants in yeast?
What are sec mutants in yeast?
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The addition of carbohydrates to ceramide yields a variety of different ___.
The addition of carbohydrates to ceramide yields a variety of different ___.
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Match the category of vesicular transport with its description:
Match the category of vesicular transport with its description:
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Which molecule is synthesized from ceramide in the Golgi apparatus?
Which molecule is synthesized from ceramide in the Golgi apparatus?
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Vesicles must recognize and fuse with any available membrane.
Vesicles must recognize and fuse with any available membrane.
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What type of transport do COPII-coated vesicles facilitate?
What type of transport do COPII-coated vesicles facilitate?
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Identify one experimental approach used to study vesicular transport.
Identify one experimental approach used to study vesicular transport.
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Synaptic transmission in neurons involves the release of chemical neurotransmitters that are stored in synaptic vesicles.
Synaptic transmission in neurons involves the release of chemical neurotransmitters that are stored in synaptic vesicles.
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What is the function of cDNA in studying vesicular transport?
What is the function of cDNA in studying vesicular transport?
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Synaptic vesicles are purified from ______ tissue for the study of protein isolation.
Synaptic vesicles are purified from ______ tissue for the study of protein isolation.
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What is the purpose of using GFP fusion proteins in research?
What is the purpose of using GFP fusion proteins in research?
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Match the following vesicle coat proteins with their respective transport functions:
Match the following vesicle coat proteins with their respective transport functions:
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Immunostaining is a technique that allows visualization of ______ protein location in fixed cells.
Immunostaining is a technique that allows visualization of ______ protein location in fixed cells.
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The mechanism of vesicular transport does not involve the removal of coat proteins before the vesicle reaches its target.
The mechanism of vesicular transport does not involve the removal of coat proteins before the vesicle reaches its target.
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Study Notes
Clathrin-Coated Vesicles
- Clathrin-coated vesicles transport molecules between the trans Golgi network (TGN), endosomes, lysosomes, and the plasma membrane.
- Vesicle formation is regulated by small GTP-binding proteins (ARF1 and Sar1) which are related to Ras and Ran GTPases.
- GTP-binding proteins recruit adaptor proteins that interact with cargo proteins and coat proteins.
- Clathrin has two polypeptide chains: heavy chain (190 kDa) and light chain (14 kDa).
- Heavy chains associate at their C-termini to form a triskelion structure.
- Light chains modulate heavy chain polymerization.
- Clathrin lattices define the shape of vesicles.
- Clathrin coated vesicles are typically 700–800 Å in diameter and contain 35–40 triskelions.
- Clathrin does not interact directly with cargo. Adaptor molecules recruit clathrin and cargo.
Vesicle Fusion
- Small GTP-binding proteins called Rab proteins direct vesicles to the correct membrane.
- Rab proteins interact with the vesicle coat and reside on the cytoplasmic surface of the vesicle.
- Tethering factors and Rab proteins mediate fusion between transport vesicles and target membranes
- Tethering factors can also bind to coat proteins and stimulate formation of complexes between SNAREs.
SNARE Proteins
- SNARE proteins mediate vesicle fusion.
- Synaptic transmission in neurons is a specialized form of regulated secretion.
- Neurotransmitters are stored in synaptic vesicles.
- Stimulation of the neuron triggers fusion of synaptic vesicles with the plasma membrane.
Visualizing Vesicular Transport
- Fluorescent microscopy allows real-time observation of vesicular transport.
- Cells can be transfected with cDNA encoding secretory proteins tagged with green fluorescent protein (GFP).
- GFP fusion proteins allow transport vesicles carrying specific proteins to be visualized by fluorescence.
- GFP might interfere with protein function and localization.
- Alternatively, fluorescent antibodies can be used to visualize intercellular protein location via immunostaining.
Transport Vesicle Coats
- Transport vesicles from the ER are coated with cytosolic coat proteins.
- Coats are removed before the vesicle reaches its target.
- Three families of vesicle coat proteins:
- COPII-coated vesicles transport from the ER to the ERGIC and Golgi.
- COPI-coated vesicles transport from the ERGIC or Golgi back to earlier compartments.
- Clathrin-coated vesicles transport between the TGN, endosomes, lysosomes, and the plasma membrane.
The Golgi Apparatus
- Glycolipids and sphingomyelin are synthesized from ceramide in the Golgi.
- Ceramides are composed of sphingosine and a fatty acid tail.
- Sphingomyelin is synthesized by transferring a phosphorylcholine group from phosphatidylcholine to ceramide.
- Glycolipids are formed by the addition of carbohydrates to ceramide.
Protein Sorting and Export in Golgi
- In the TGN, molecules are sorted and packaged into transport vesicles.
- Proteins that need to stay in the Golgi contain signals that prevent packaging and transport.
- Transport from the Golgi to the cell surface can occur via three routes:
- Direct transport to the plasma membrane
- Recycling endosomes
- Regulated secretory pathways
- Regulated pathways include release of hormones and neurotransmitters.
- These proteins aggregate in the TGN and are packaged in secretory granules.
- The granules store their contents until signals direct their fusion with the plasma membrane.
Membrane Domains
- Polarized cells of epithelial tissue have apical and basolateral domains with specific proteins.
- Proteins leaving the TGN must be selectively packaged and transported to the correct domain.
Studying Vesicular Transport
- Understanding the mechanisms that control vesicular transport is a major area of research.
- Three approaches have been used for studying vesicular transport:
- Isolation of yeast mutants defective in protein transport and sorting
- Reconstitution of vesicular transport in cell-free systems
- Biochemical analysis of synaptic vesicles
Yeast Mutants
- Yeast mutants can be defective at various stages of protein secretion (sec mutants), or are unable to transport proteins to the vacuole, or retain resident ER proteins.
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Description
Explore the intricate processes of clathrin-coated vesicles and vesicle fusion in cellular transport. This quiz covers the roles of GTP-binding proteins, adaptor proteins, and the structure of clathrin in the formation and function of vesicles. Test your understanding of key concepts in cellular biology related to vesicular transport.
